net: selftests: add getsockopt_iter regression tests

Add a single kselftest covering the proto_ops getsockopt_iter
conversions for AF_NETLINK and AF_VSOCK, using one fixture per protocol:

netlink:

NETLINK_PKTINFO covers the flag-style int path (exact size, oversize
clamp, undersize -EINVAL); NETLINK_LIST_MEMBERSHIPS covers the
size-discovery path that always reports the required buffer length back
via optlen, even when the user buffer is too small to receive any group
bits.

vsock:
SO_VM_SOCKETS_BUFFER_SIZE covers the u64 path (exact size, oversize
clamp, undersize -EINVAL).

Each fixture also exercises an unknown optname and a bogus level so
the returned-length / errno semantics preserved by the sockopt_t
conversion are pinned down.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260501-getsock_one-v1-3-810ce23ea70e@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/Makefile

@@ -176,6 +176,7 @@ TEST_GEN_PROGS := \
 	bind_timewait \
 	bind_wildcard \
 	epoll_busy_poll \
+	getsockopt_iter \
 	icmp_rfc4884 \
 	ipv6_fragmentation \
 	proc_net_pktgen \

tools/testing/selftests/net/getsockopt_iter.c

@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Quick test for getsockopt{_iter} tests.
+ *
+ * Each fixture targets one converted protocol and pins down the
+ * returned-length / errno semantics across buffer-size variations,
+ * an unknown optname and a bogus level.
+ *
+ * - netlink: NETLINK_PKTINFO covers the flag-style int path; the
+ *   NETLINK_LIST_MEMBERSHIPS cases cover the size-discovery path
+ *   that always reports the required buffer length back via optlen,
+ *   even when the user buffer is too small to receive any group bits.
+ * - vsock:   SO_VM_SOCKETS_BUFFER_SIZE covers the u64 path.
+ *
+ * Author: Breno Leitao <leitao@debian.org>
+ */
+
+#include <errno.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+#include <linux/vm_sockets.h>
+#include <sys/socket.h>
+#include "kselftest_harness.h"
+
+#ifndef AF_VSOCK
+#define AF_VSOCK 40
+#endif
+
+/* ---------- netlink ---------- */
+
+FIXTURE(netlink)
+{
+	int fd;
+};
+
+FIXTURE_SETUP(netlink)
+{
+	int group = RTNLGRP_LINK;
+
+	self->fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
+	if (self->fd < 0)
+		SKIP(return, "AF_NETLINK socket: %s", strerror(errno));
+
+	/* Joining a multicast group grows nlk->ngroups so the
+	 * NETLINK_LIST_MEMBERSHIPS path has a non-zero size to report.
+	 */
+	if (setsockopt(self->fd, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP,
+		       &group, sizeof(group)) < 0)
+		SKIP(return, "NETLINK_ADD_MEMBERSHIP: %s", strerror(errno));
+}
+
+FIXTURE_TEARDOWN(netlink)
+{
+	if (self->fd >= 0)
+		close(self->fd);
+}
+
+TEST_F(netlink, pktinfo_exact)
+{
+	int val = -1;
+	socklen_t optlen = sizeof(val);
+
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_NETLINK, NETLINK_PKTINFO,
+				&val, &optlen));
+	ASSERT_EQ(sizeof(int), optlen);
+	ASSERT_TRUE(val == 0 || val == 1);
+}
+
+TEST_F(netlink, pktinfo_oversize_clamped)
+{
+	char buf[16] = {};
+	socklen_t optlen = sizeof(buf);
+
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_NETLINK, NETLINK_PKTINFO,
+				buf, &optlen));
+	ASSERT_EQ(sizeof(int), optlen);
+}
+
+TEST_F(netlink, pktinfo_undersize)
+{
+	char buf[2] = {};
+	socklen_t optlen = sizeof(buf);
+
+	ASSERT_EQ(-1, getsockopt(self->fd, SOL_NETLINK, NETLINK_PKTINFO,
+				 buf, &optlen));
+	ASSERT_EQ(EINVAL, errno);
+}
+
+TEST_F(netlink, list_memberships_size_discovery)
+{
+	socklen_t optlen = 0;
+	char dummy;
+
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_NETLINK,
+				NETLINK_LIST_MEMBERSHIPS,
+				&dummy, &optlen));
+	ASSERT_GT(optlen, 0);
+	ASSERT_EQ(0, optlen % sizeof(__u32));
+}
+
+TEST_F(netlink, list_memberships_full_read)
+{
+	__u32 buf[64] = {};
+	socklen_t optlen = sizeof(buf);
+
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_NETLINK,
+				NETLINK_LIST_MEMBERSHIPS,
+				buf, &optlen));
+	ASSERT_GT(optlen, 0);
+	ASSERT_LE(optlen, sizeof(buf));
+	ASSERT_EQ(0, optlen % sizeof(__u32));
+}
+
+TEST_F(netlink, bad_level)
+{
+	int val;
+	socklen_t optlen = sizeof(val);
+
+	ASSERT_EQ(-1, getsockopt(self->fd, SOL_SOCKET + 1, NETLINK_PKTINFO,
+				 &val, &optlen));
+	ASSERT_EQ(ENOPROTOOPT, errno);
+}
+
+TEST_F(netlink, bad_optname)
+{
+	int val;
+	socklen_t optlen = sizeof(val);
+
+	ASSERT_EQ(-1, getsockopt(self->fd, SOL_NETLINK, 0x7fff,
+				 &val, &optlen));
+	ASSERT_EQ(ENOPROTOOPT, errno);
+}
+
+/* ---------- vsock ---------- */
+
+FIXTURE(vsock)
+{
+	int fd;
+};
+
+FIXTURE_SETUP(vsock)
+{
+	self->fd = socket(AF_VSOCK, SOCK_STREAM, 0);
+	if (self->fd < 0)
+		SKIP(return, "AF_VSOCK socket: %s", strerror(errno));
+}
+
+FIXTURE_TEARDOWN(vsock)
+{
+	if (self->fd >= 0)
+		close(self->fd);
+}
+
+TEST_F(vsock, buffer_size_exact)
+{
+	uint64_t val = 0;
+	socklen_t optlen = sizeof(val);
+
+	ASSERT_EQ(0, getsockopt(self->fd, AF_VSOCK,
+				SO_VM_SOCKETS_BUFFER_SIZE,
+				&val, &optlen));
+	ASSERT_EQ(sizeof(uint64_t), optlen);
+	ASSERT_GT(val, 0);
+}
+
+TEST_F(vsock, buffer_size_oversize_clamped)
+{
+	char buf[16] = {};
+	socklen_t optlen = sizeof(buf);
+
+	ASSERT_EQ(0, getsockopt(self->fd, AF_VSOCK,
+				SO_VM_SOCKETS_BUFFER_SIZE,
+				buf, &optlen));
+	ASSERT_EQ(sizeof(uint64_t), optlen);
+}
+
+TEST_F(vsock, buffer_size_undersize)
+{
+	char buf[4] = {};
+	socklen_t optlen = sizeof(buf);
+
+	ASSERT_EQ(-1, getsockopt(self->fd, AF_VSOCK,
+				 SO_VM_SOCKETS_BUFFER_SIZE,
+				 buf, &optlen));
+	ASSERT_EQ(EINVAL, errno);
+}
+
+TEST_F(vsock, bad_level)
+{
+	uint64_t val;
+	socklen_t optlen = sizeof(val);
+
+	ASSERT_EQ(-1, getsockopt(self->fd, SOL_SOCKET + 1,
+				 SO_VM_SOCKETS_BUFFER_SIZE,
+				 &val, &optlen));
+	ASSERT_EQ(ENOPROTOOPT, errno);
+}
+
+TEST_F(vsock, bad_optname)
+{
+	uint64_t val;
+	socklen_t optlen = sizeof(val);
+
+	ASSERT_EQ(-1, getsockopt(self->fd, AF_VSOCK, 0x7fff,
+				 &val, &optlen));
+	ASSERT_EQ(ENOPROTOOPT, errno);
+}
+
+TEST_HARNESS_MAIN